Fatigue Life Analysis Of The Critical Components In A Large Reciprocating Compressor

Aiming at the problem that the critical components such as crankshaft,connecting rods and crossheads in a large reciprocating compressor get fatigue failure easily in working process,the fatigue life is systematically studied in this paper respectively from modal analysis,fatigue life prediction,fatigue life characteristics and fatigue test design taking crankshaft-connecting rod system(including crankshaft,connecting rod and crosshead)in a large reciprocating compressor as the example.Firstly,in order to judge whether the natural frequency of the crankshaft-connecting rod system will overlap with the driving frequency of the compressor,a modal analysis with finite element method is carried out on the assembly model of the crankshaft-connecting rod system.The results show that the first order natural frequency of the crankshaftconnecting rod system is 328.86 Hz that is much larger than the driving frequency of the compressor 16 Hz,which means that the crankshaft-connecting rod system will not resonate with the whole machine in working process,so the reliability of the critical components is preliminarily verified.Then,the fatigue life of crankshaft,connecting rods and crossheads is calculated respectively with S-N method based on the finite element static structural analysis under 6 angles in one cycle.The results show that all the critical components studied meet strength requirements and the weak zone of static strength and fatigue strength are according with the empirical conclusions,thus an efficient and accurate fatigue life calculation process for the critical components in a large reciprocating compressor is formed.On the basis of the research above,the fatigue life characteristics of the critical components are studied respectively from the aspects of processing technology and structure through finite element method.Firstly,the influences of material strength and surface processing technology on crankshaft fatigue life are studied.The results show that the fatigue life can be effectively enhanced by selecting high strength materials to manufacture crankshafts and refining crankshaft surface treatment.Secondly,against the stress concentration appeared at the connecting rod bolt under-head fillet in static structural analysis,the elliptic fillet is proposed to be used as the bolt under-head fillet structure instead of traditional fillet,and the influences of the elliptic fillet structure parameters on fillet stress concentration and fillet fatigue life are studied,providing a theoretical guidance for the fatigue design of the critical components in engineering.Finally,in view of the problems that the connecting rod bush is easy to wear in the working process and the life could not be calculated by finite element method,An wear test scheme including on-line monitoring and off-line testing for the connecting rod bushing in a large reciprocating compressor(including big end bushing and the small end bushing)is designed,providing guidance for studying the relationship between the working condition of the large reciprocating compressor and the wear or fatigue life of the bushing.